1. Field of the Invention
The present invention relates to a Bi-Pb-Sr-Ba-Ca-Cu-O system superconductor which is based on a Bi-Sr-Ca-Cu-O system superconductor which attracts attention since it exhibits superconductivity at 77K or higher, in some cases at 100K or higher.
2. Description of the Related Art
The National Institute for Metals reported that in a sintered body of Bi.sub.1 Sr.sub.1 Ca.sub.1 Cu.sub.2 O.sub.x, electrical resistance began to drop at 120K, sharply dropped till 107K and became zero at about 75K. The reported material contains two superconductive phases one of which has the superconductive transition termination temperature of about 105K which temperature was obtained by extrapolation of the measured data (high T.sub.c phase) and the other of which has the superconductive transition termination temperature of about 75K (low T.sub.c phase) and the whole material does not necessarily consists of the high T.sub.c phase. However, the Meissner effect was observed with this material.
The reported superconductive material contains no rare earth element and is more stable to water and the like than the Y-Ba-Cu-O system superconductor.
Takano et al reported that the addition of lead (Pb) to the Bi-Sr-Ca-Cu-O system superconductor increased the volume fraction of high T.sub.c phase having T.sub.c of about 107K to the range between 80% and about 100% (Jpn. J. Appl. Phys., 27, 1988, L1041-1043).
Most of the reported Bi-Sr-Ca-Cu-O system superconductors contain both the high T.sub.c phase and the low T.sub.c phase. Although the addition of lead increases the fraction of high T.sub.c phase, the production conditions are not made clear, and reproducibility has to be improved.